Cement-based fire door core

ABSTRACT

The present invention describes an improved building material composition, useful for example as a fire door core. The building material of the present invention is prepared by compressing an aqueous mixture of expanded perlite and a fast setting, cementitious composition consisting essentially of a hydraulic cement, preferably Portland cement, and a pozzolan additive selected from the group consisting of metakaolin, VCAS and mixtures thereof, and preferably also includes an organic binder and a fibrous reinforcement.

TECHNICAL FIELD

This invention is in the field of building materials, especiallyfire-resistant building materials. Specifically, this inventiondescribes a building material made from a particular fast settingcementitious composition and having utility as an improved corecomposition for fire doors.

BACKGROUND OF THE INVENTION

Fire doors are generally made for the purpose of stopping or delayingthe transfer of thermal energy (i.e., heat), from one side of the doorto the other side. Current fire-resistant doors generally contain afire-resistant core usually encased in a door-shaped shell, wherein theshell is made from various materials generally known to those ofordinary skill in the art. The core is customarily bonded or glued toboth inside surfaces of the shell.

Fire doors, as used in residential, commercial, and industrialapplications, typically are employed in conjunction with fire walls toprovide fire protection between different zones of a structure, andparticularly to isolate high fire risk areas of a building from theremainder of the structure, such as the garage of a dwelling from itsliving quarters. Fire doors usually are not capable of indefinitelywithstanding the high temperature conditions of a fire but, rather, aredesigned to maintain the integrity of the firewall for a limited time topermit the occupants of a building to escape and to delay the spread offire until fire control equipment can be brought to the scene.

Various tests have been designed for fire doors and are based onfactors, such as the time that a given door would withstand a certaintemperature while maintaining its integrity, and hose stream tests whichinvolve the door's ability to withstand the forces of a high pressurewater stream. The American Society for Testing Materials (ASTM) hasdevised tests to establish fire door standards and these standards areincorporated into building codes and architectural specifications. Onesuch standard, ASTM Method E 152, requires a door to maintain itsintegrity for period ranging up to 1.5 hours while withstandingprogressively higher temperatures and erosive effects of a high pressurestream of water from a fire hose at the conclusion of the heat (fire)exposure.

Considerations in fire door design, in addition to retarding the advanceof fire, include the cost of raw materials and the cost of fabrication.Furthermore, the weight of the door is important, both from thestandpoint of ease of handling and cost of transportation. The strengthof the door is also a significant factor, since fire doors must pass theabove-described water stream test as well as have the requisite strengthto withstand normal use and abuse.

Fire-resistant doors have been made using a variety of constructions andutilizing a number of different materials, including wood, metal, andmineral materials. Early forms of fire doors simply comprised woodencores faced with metal sheeting. Although wood of ample thickness is aneffective fire and heat retardant, doors of such construction tend to beheavy and are expensive to fabricate and transport.

Mineral fibers have also been employed in the manufacture of fire doors.The core of a commercial metal fire door principally comprises acomposition including mineral fibers and a binder. Such doors suffer,however, from a lack of strength, and handling the friable cores resultsin the production of irritating dust particles during the manufacturingprocess.

Some fire-resistant cores are constructed using such materials asperlite (which functions as an inorganic filler), gypsum (whichfunctions as the fire resistant material), cement (which functions as afurther fire resistant material and counteracts shrinkage of the core),a solution of polyvinyl alcohol and water (which also acts as a binderand increases the viscosity of the mixture of ingredients while alsohydrating the gypsum) and fiberglass (which functions as a reinforcingmaterial). See for example U.S. Pat. No. 4,159,302, the disclosure ofwhich is incorporated herein by reference.

It has also been proposed to make fire doors wherein the core comprisesparticles of expanded perlite, which are bound together by the use ofvarious hydraulic binders including gypsum, cement, and inorganicadhesive material. In order to provide sufficient strength, particularlyto withstand handling of the core during manufacture, the core typicallyis compressed to compact the mixture to a relatively high density,resulting in a heavy door.

Other fire doors have included conventional gypsum wallboard panels as acore material. However, in order to produce sufficient fire resistance,the thickness required of the wallboard is such as to result in anexcessively heavy door. Furthermore, internal structural members such asrails or mullions have been found necessary to support and strengthenwallboard panels. The need for such reinforcing elements increases thecost of materials and assembly of such doors. In addition to theabove-mentioned considerations, fire doors must, in order to becommercially acceptable, also have other properties that are related tothe manufacture, installation and service of the fire door.

Fire door cores that contain a significant proportion of gypsum may losetheir fire resistant capabilities in the course of a fire. As is wellknown, gypsum calcines when contacted with sustained heat. During afire, calcination of the gypsum in a door core may cause the core tolose strength and integrity, especially when thereafter exposed towater, such as a high pressure stream of water from a hose. Thus, thefire resistance and structural integrity of such a door core isdegraded. Furthermore, current fire-resistant door cores containinggypsum exhibit high water absorption rates thereby increasing both theirsize and density.

U.S. Pat. No. 6,340,389 describes a fire door cores made from expandedperlite, a fireproof binder such as an alkali metal silicate, fire clayor vermiculite, and optionally one or more viscosity-enhancingcomponents, fiberglass, or both. The fire door core is made using asemi-continuous batch press method wherein water, the expanded perlite,the fireproof binder, fire clay or vermiculite are mixed; and the wetmixture is compressed in a mold, and the compressed mixture dried.

U.S. Pat. No. 6,846,358 describes an improved building materialcomposition, useful for example as a fire door core and to improvedmethods of making this composition. The building material is preparedfrom an aqueous mixture of expanded perlite and a fast setting,cementitious composition consisting essentially of a hydraulic cementhaving (1) a Portland cement and (2) a calcium aluminate cement, whichcomposition is molded and shaped into a fire door core.

There continues to be a demand for building materials suitable for useas fire door cores. In order to meet this commercial need, a door coreshould maintain its strength and integrity and have acceptable hosestream resistance after being exposed to heat. Additionally, to enhanceits commercial viability the door core should be easily manufacturedusing techniques well-known in the art. The present invention fulfillsthese commercial needs by using an improved fast setting cementitiouscomposition as the major structural component of the composition.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to a building material compositionwhich can be used as a fire door core. Building material compositions(e.g., fire door cores) of the present invention can meet and in somecases may exceed the fire-resistant capabilities of current fire doorcores. One characterizing feature of the building material composition(e.g., fire door core) of the present invention is that it issubstantially free of set gypsum. The building material composition(e.g., fire door core) of the present invention comprises, as its mainconstituent, an expanded perlite and as a second, normally minor, thoughessential constituent, a cured fast setting, cementitious composition.The ingredients used to prepare the building material composition, uponhydration with water, can be molded, shaped and cured into a desiredshape, such as for a fire door core.

The fast setting cementitious composition of this invention consistsessentially of a mixture of (1) a hydraulic cement component, andparticularly a Portland cement (ordinary Portland cement or OPC) and (2)a pozzolan additive selected from the group consisting of metakaolin, aVitreous Calcium Aluminosilicate (known as VCAS) and mixtures thereof.Upon being mixed with water in an amount within the range of about 15 to50 percent by weight, more usually within the range of about 20 to 40wt. %, and most often within the range of about 25 to 35 wt. %, based onthe weight of the dry mixture of the constituents, the resulting moistcomposition exhibits a suitable setting time for manufacturing fire doorcores.

The fire door core may also contain, as minor optional (though oftenpreferred) components, an organic binder, most preferably polyvinylalcohol (i.e., a polyvinyl acetate which is substantially fullyhydrolyzed), and a fibrous reinforcement, most preferably chopped glassfibers.

Still other optional (minor) ingredients include an alkali metalsilicate, unexpanded vermiculite, and clay.

Preferably, the hydraulic cement component and particularly a Portlandcement (OPC), of the fast setting cementitious composition is present ina weight ratio relative to the pozzolan additive (PA), i.e., OPC:PAwithin the range of about 3:1 to 30:1 and more preferably, within therange of about 4:1 to 15:1.

The building material or fire door core composition of the presentinvention can be made by admixing the expanded perlite, the fastsetting, cementitious composition, an optional organic binder, anoptional fibrous reinforcement and other optional additives which mayalso be used, with an amount of water at least sufficient to provide amoist, (damp) mixture of the ingredients and sufficient to set the fastsetting cementitious composition. Water preferably is added in an amountof between about 20 to 40 wt % of the weight of the dry ingredients inthe composition. The composition can then be molded into the desiredshape, including a desired thickness, and density for the fire doorcore.

DETAILED DESCRIPTION OF THE INVENTION

The building material composition, preferably in the form of a fire doorcore, of the present invention comprises as a major component expandedperlite and as a second, generally minor (though essential), component acured fast setting cementitious composition which consists essentiallyof a mixture of (1) a hydraulic cement component, particularly Portlandcement (OPC), and (2) a pozzolan additive selected from the groupconsisting of metakaolin, VCAS and mixtures thereof.

For convenience, the building material composition is typically definedin terms of its constituent components notwithstanding the fact that atleast in the case of the two components of the fast setting cementitiouscomposition there is understood to be a chemical interaction that occursduring the setting and curing of the composition as the final product isformed.

The main constituent of the fire door core of the present invention isan expanded perlite. Expanded perlite is present in the door core in anamount of about 65 to 85 weight percent based on the total weight of theother dry ingredients. Expanded perlite is available in various forms asis well known to those of ordinary skill in the art. Speaking generally,expanded perlite can be formed by heating moisture-containing,natural-occurring perlite ore at a temperature within the range of about1,500° to 2,000° F. (815° to 1093° C.) Such heat treatment explodes orexpands the perlite to, for example, 15-20 times its original volume.Commercially available forms of expanded perlite known as cryogenic,plaster and concrete aggregate are exemplary of materials that can beused in the practice of the present invention. Expanded perlite,suitable for use in the present invention, generally has a density fromabout 2 to about 11 lbs per cubic foot (pcf). Usually, an expandedperlite with a density of about 4 to 8 pcf will be used, particularly anexpanded perlite such as a 6.5 pcf perlite. Furthermore, the particlesize of the expanded perlite used in making the building materialcomposition can vary over a wide range. Generally an expanded perlitehaving a particle size distribution that passes through a 30 mesh screenand is retained on a 100 mesh screen (U.S. Standard Sieve Series) shouldbe suitable.

The expanded perlite functions as a non-combustible, compactable fillerwhich imparts light weight to the set (cured) composition, and alsorelatively high strength as compared to other means which could be usedto impart light weight to the set composition, for example, such as byintroducing air voids into the set composition by foaming the mixture ofingredients from which the set composition is made.

To optimize strength properties of the core, those forms of expandedperlite which are more resistant to being compressed or compactedrelative to other more compactable forms of perlite should preferably beused. It has been observed that various forms of perlite are less spongythan others. The less spongy the perlite, the greater its resistance tobeing compressed and the greater the anticipated strength of the coremade from the perlite. Conversely, the more spongy the perlite, the morereadily it is compressed and the lower the anticipated strength of thecore. See U.S. Pat. No. 4,159,302 for additional discussion.

While generally present as a minor component of the building materialcomposition, the set or cured fast setting cementitious component, whichconsists essentially of a mixture of (1) a hydraulic cement component,particularly a Portland cement (e.g., OPC), and (2) a pozzolan additiveselected from the group consisting of metakaolin, VCAS and mixturesthereof, constitutes the principal constituent holding the buildingmaterial composition together as a unitary construction. The fastsetting cementitious composition is added to form the building materialcomposition in an amount of 10 to 45 percent by weight, more usuallywithin the range of about 15 to 40 wt. %, and most often within therange of about 18 to 30 wt. %, of the weight of the dry mixture of theconstituents used to make the composition.

Portland cements represent a class of hydraulic cements that contain asubstantial quantity of calcium silicate with only minor quantities ofaluminates, namely, tricalcium aluminate and a calcium aluminoferrite.As known to those skilled in the art, Portland cements are produced byheating, to incipient fusion, an intimate mixture of calcareous andargillaceous, or other siliceous, aluminious, and iron-oxide-bearingmaterials so as to form a clinker. The clinker then is pulverized and asmall amount of calcium sulphate, usually gypsum, is added to improvethe setting characteristics of the finished cement.

Portland cements are commonly characterized by type in accordance withstandards developed by the American Portland Cement Association and thestandards and designations applied there are used in characterizingPortland cements herein (Types I, IA, II, IIA, I/II, III, IIIA, IV andV). The Portland cement constituent of the present invention can beanyone of these wide variety of Portland cement types, though thenormal, general purpose Type I Portland cement (OPC) is usuallysuitable. As noted, such cements principally contain calcium silicateand have a relatively low alumina content, i.e., less than 10 wt. %.Portland cement compositions typically contain more than 60% CaO andless than 3% aluminum and 1.5% sulfur.

The second component of the fast setting cementitious component is apozzolan additive selected from the group consisting of metakaolin, VCASand mixtures thereof. These pozzolans are non-cementitious on their own,but react with calcium hydroxide produced during the hydration of ahydraulic cement, such as Portland cement, to form additionalcementations compounds, such as calcium silicate hydrates andalumino-silicate hydrates, which fill in pores in the cured cement anddensify the concrete matrix.

Metakaolin is a dehydroxylated form of kaolinite. Metakaolin is formedby heating (calcining) kaolinite (e.g., china clay or kaolin clay)between about 500 to 800° C., more usually between 650 to 700° C. Thedehydoxylation that occurs at this temperature produces an amorphous,highly pozzolanic material. Highly reactive metakaolin is available fromAdvanced Cement Technologies, LLC, Blaine, Wash., USA and from BASF(previously Engelhard Corporation), New Jersey, USA.

VCAS (Vitreous Calcium Aluminosilicate) pozzolan is available from VitroMinerals Inc, Canton Mich. and is produced from glass fibermanufacturing waste as described in U.S. Pat. No. 6,776,838. A moltenblend of ground silica, lime and alumina compounds is solidified byquench cooling and ground to a fine white powder.

The hydraulic cement, e.g., Portland cement component (OPC) and thepozzolan additive selected from the group consisting of metakaolin, VCASand mixtures thereof (PA) are present in the fast setting cementitiouscomponent of the building material composition in a weight ratio(OPC:PA) within the range of about 3:1 to 30:1 and more preferably,within the range of about 4:1 to 15:1. A preferred formulation includesPortland cement in a weight ratio to the pozzolan additive of about10:1.

The set cementitious composition component imparts to the buildingmaterial composition, such as to a fire door core, good water resistantproperties and high compressive strength. Accordingly, the setcementitious composition helps to maintain the integrity of the firedoor core when the door is exposed to the wetting and the pressure of ahose stream. In addition, the set cementitious composition functions asa shrink resistant material in the core when it is exposed to fire.

The building material composition, e.g., fire door core composition, ofthe present invention does not require set gypsum as a significantstructural component and thereby avoids problems associated with currentcompositions used as door cores which rely primarily on set gypsum,i.e., the door core of the present invention is substantially free ofset gypsum. In fact, the building material composition of this inventionis preferably free from added gypsum altogether. Current door cores thatcontain gypsum cannot be considered fire-proof, at best, they can onlybe considered fire-resistant. Fire door cores, that contain gypsum as astructural component, have the problem that, when subjected to extendedheating, the gypsum calcines and the door core loses its strength andintegrity. Thus, when the door core thereafter is contacted by water,typically in the form of a high pressure stream of water from a hose,the integrity of the door is compromised because the calcined gypsum iswashed away. The fire door core of the present invention is expected tomeet or exceed the capabilities of current fire-resistant cores madewith set gypsum in standard fire tests for residential andnon-residential use. The fire door core of the present invention also isexpected to exceed the capabilities of fire-resistant door corescontaining set gypsum in maintaining strength and integrity followingprolonged heat, even when exposed to water.

The building material composition, especially the fire door core, of thepresent invention can also optionally include, and preferably doescontain, still additional components, particularly an organic binder anda fibrous reinforcement, to achieve desired flexural and compressivestrength and general handling characteristics. While desired strengthcharacteristics may be achieved without the use of the organic binderand fibrous reinforcement, the absence of these optional ingredientstends to increase the density of the product at an equivalent level ofproperties. Thus, use of an organic binder and fibrous reinforcement areoften preferred.

The organic binder is preferably a synthetic material such as polyvinylalcohol, polyvinyl acetate, polymers of vinyl acetate and ethylene,polymers of styrene and butadiene, and acrylic resins.

The organic binder is typically a material which is dispersible orsoluble in water. Indeed, in many cases the organic binder will beintroduced into the mixture of ingredients used to form the buildingmaterial composition as an aqueous solution or as an aqueous dispersionduring the preparation of the building material composition, with thewater introduced with the organic binder supplying a portion of thewater required by the process for making the ultimate product, i.e., forhydrating the fast setting cementitious component as the compositionsets and cures.

A preferred organic binder is polyvinyl alcohol, a well knowncommercially available water soluble material. Speaking generally,polyvinyl alcohol is prepared by hydrolyzing polyvinyl acetate. Thesource of the polyvinyl alcohol is preferably a substantially completelyhydrolyzed form of polyvinyl acetate, that is, about 97 to 100%hydrolyzed polyvinyl acetate. A suitable polyvinyl alcohol can becold-water insoluble. In this case, solutions can be prepared atelevated temperatures, for example, at temperatures of about 140° to205° F. (60° to 96° C.). Commercially available polyvinyl alcohols foruse in the composition of the present invention are available from theDupont Company under the trademark “Elvanol.” Examples of such productsare Elvanol, Grades 90-50, 71-30, 75-15, 72-60 and 70-06. When used, theorganic binder is generally included in the building materialcomposition in an amount of up to about 5 percent by weight, such asfrom 1 to 5 percent, usually about 3 percent or less, such as from 1 to2 percent, each of these percents based on the total weight of the dryingredients used to form the building material composition, e.g., thefire door core.

The fibrous reinforcement also imparts flexibility and impact-resistantproperties to the set composition, and also provides better handlingproperties to improve resistance to cracking or breakage during shipmentor processing of the door core. As fibrous reinforcements glass fibersare preferred. Examples of other fibrous reinforcements that can besubstituted for glass fibers or used in combination therewith aremineral fibers (such as Wollastonite and mineral wool), sisal fibers,graphite fibers, and synthetic fibers such as, for example, polyolefinfibers, such as polyethylene fibers and polypropylene fibers, rayonfiber and polyacrylonitrile fiber. The fiber reinforcement also mayimprove the material handling properties of the wet mixture, e.g., thewet door core mixture and especially the wet composite, e.g., the wetdoor core. Typically, when used, the amount of fiber reinforcement is nomore than about 2 percent by weight, such as from 0.1 to 2 percent,usually about 1 percent or less, such as from 0.2 to 1 percent, moreusually, from about 0.2 to about 0.7 percent, each of these percentsbased on the total dry weight of the various ingredients used to formthe building material composition, e.g., the fire door core.

Still other optional ingredients also may be included in the mixture ofingredients used to prepare the building material composition or firedoor core, such as unexpanded verimculite (to enhance fire resistantproperties of the set composition and to counteract any tendency toshrink at elevated temperatures thereby imparting improved dimensionalstability properties to the set composition during exposure to heat),clay (to improve fire resistant and high temperature, dimensionalstability properties), and possibly a defoamer. These optionaladditional ingredients do not prevent the composition from fulfilling,and in most cases enhance, its use in fire resistant applications.

Clays are natural, earthy, fine-grained materials, most of which exhibitplastic characteristics when moistened with limited amounts of water. Ingeneral, clays comprise primarily alumina, silica and water and may alsocontain to a lesser extent iron, alkali, alkaline earth and othermetals. The various types of clays in general have particles ranging insize from fractions of a micron to about 40 microns, although somematerials having particles of an even larger size are also consideredclays. It should be understood that materials which do not have all ofthe above characteristics, but which nevertheless are generally referredto as clays because they have one or more of the above characteristicsare included within the term “clay” as used herein. Examples of thetypes of clay that can optionally be utilized are: kaoliniticclays—including, for example, kaolin (also referred to as china or paperclays), ball clay, fireclay, and flint clay, which clays are comprisedpredominantly of the clay mineral kaolinite.

The building material composition when used as a fire door core inaccordance with the present invention is expected to provide severaladvantages over currently used fire-resistant door cores, including butnot limited to, increased production capabilities using methods known tothose of ordinary skill, decreased raw material consumption, strongeradhesion to door shells, sufficient thermal integrity to allow use ofthermosetting binders for attaching door skins, increased tensile andflexural strength, superior hose stream resistance, decreased weight,and better shaping and handling characteristics.

The phrase “consisting essentially of” when used in connection with thepresent invention and in the claims is intended to exclude not only theuse of ingredients that would destroy the fire resistant property of thecomposition, but also to exclude the addition of calcined gypsum inamounts in excess of about 5% by weight. Preferably, calcined gypsum isnot added to the mixture of ingredients used to form the composition inexcess of about 2% by weight.

As to amounts of ingredients preferably utilized in the practice of thepresent invention, the set building material composition comprises theset product of an aqueous mixture, based on the total dry weight of theingredients used in the mixture, of:

-   -   (A) about 65 to about 85 wt. % of expanded perlite;    -   (B) about 15 to about 50 wt. % of the fast setting cementitious        component;    -   (C) up to 5% and preferably about 1 to about 5 wt. % of an        organic binder;    -   (D) up to about 2 wt. % and preferably about 1% of fibrous        reinforcements,    -   (E) 0 to about 4 wt. % of clay; and    -   (F) 0 to about 4 wt. % of unexpanded vermiculite.

In a more preferred form, the aforementioned aqueous mixture includes,based on the total dry weight of the various ingredients in the mixture:

-   -   (A) about 65 to about 85 wt. % perlite;    -   (B) about 20 to about 40 wt. % of the fast setting cementitious        component;    -   (C) at least about 1.5 wt. % of an organic binder;    -   (D) at least about 0.2 wt. % and up to 1% of a fibrous        reinforcement    -   (E) 0 to about 4 wt. % of unexpanded vermiculite; and    -   (F) 0 to about 4 wt. % of clay.

The building material composition, e.g., a fire door core, of thepresent invention is manufactured by combining the various components(most of which are generally supplied as dry ingredients) with water toform a wet mixture, e.g., a wet door core mixture. The amount of waterto use in making a set composition, e.g., a door core, is at leastsufficient to provide the stoichiometric amount of water needed to causethe setting (curing) of the fast setting cementitious component. It isgenerally desirable to include an amount of water in excess of thestoichiometric amount. In certain embodiments, it may be preferred touse only an amount of water sufficient to provide a damp (moist) mixtureof the ingredients. In alternative embodiments, higher amounts of watercan be used, for example, amounts that produce a moldable slurry of thedry, solid ingredients. In most cases, a set composition, such as a doorcore, can be prepared readily using from about 15 to about 60% by weightof water based on the dry weight of the various ingredients comprisingthe mixture. Usually an amount of water in the range of about 15 to 45wt. %, more usually within the range of 20 to 40 wt. %, of the dryweight of the mixture of ingredients, should be suitable for preparingthe wet composition, e.g., a wet door core mixture.

The wet mixture, e.g., the wet door core mixture, then is molded andpressed as needed to form a wet composite, e.g., a wet door core. Thewet composite, e.g., wet door core, then is dried to form the buildingmaterial composition, e.g., the fire door core, of the invention.

As described herein, the wet mixture, e.g., the wet door core mixture,and the wet composite, e.g., wet door core, preferably have a solidsconcentrations, that provide ease of handling, i.e., the solidsconcentrations are not so high as to cause difficulty in the mixingand/or transferring of the wet mixture from mixer to mold, and is not solow as to yield a wet composite, e.g., a wet door core, that lacksdimensional stability. Therefore, the form, i.e., whether as a dry solidor as an aqueous mixture, of an individual component used in preparingthe mixture from which the building material composition is prepared,typically is selected so that the solids concentration of the wetmixture, e.g., the wet door core mixture and the wet composite, e.g.,the wet door core, need not be adjusted. However, additional water maybe added to obtain a wet mixture, e.g., a wet door core mixture and thena wet composite, e.g., a wet door core, having a desired handlingproperty, if necessary.

An alkali metal silicate can also be used as an optional ingredient inthe mixture for forming the building material composition. The alkalimetal silicate can be used in an amount of from 0% up to about 15percent of the total dry weight of the mixture of ingredients used toprepare the composition, e.g., of the fire door core. Preferably, thealkali metal silicate is sodium silicate or potassium silicate, morepreferably it is sodium silicate. Sodium silicate used in the fire doorcore of the invention typically has a molar ratio of silica to sodiumoxide of from about 2.5:1 to about 4:1. Preferably, the ratio of silicato sodium oxide is about 3.22:1. When used, the sodium silicate isprovided to the mixture generally as an aqueous solution. The solidsconcentration in this aqueous silicate solution (along with anyadditional water used to make the wet mixture of ingredients for formingthe fire door composition) must yield a wet composite, e.g., a wet doorcore, that is easy to handle, both during molding operations and afterthe wet composite, e.g., the wet door core, is removed from the mold,and is economically dried.

Typically, the solids content of sodium silicate solution optionallyused in this invention is between about 30 and about 50 weight percent,more usually between about 34 and 44 weight percent, and most oftenabout 37 weight percent solids. Silicate solutions having lower orhigher solids concentrations also can be used. A commercial example of asolution of sodium silicate and water is ‘N’ grade sodium silicatesolution marketed by PQ Corporation of Valley Forge, Pa. This solutionhas a molar ratio of silica to sodium oxide of 3.22:1 and a solidsconcentration of 37 weight percent.

Optionally, one or more dispersing agents or plasticizers can be used incombination with the optional alkali silicate additive for producing thebuilding material composition, e.g., the fire door core, of the presentinvention to facilitate processing of the wet mixture. Specificconcentrations, amounts, and identity of the optional dispersing agentor plasticizer will be apparent to skilled practitioners who recognizethat these parameters will vary depending on external preferences suchas price and availability of the additional components and that thedescribed embodiments do not limit the scope of the claimed invention.

Use of a dispersing agent or plasticizer also may enhance certainphysical properties of the building material composition, e.g., certainproperties of the fire door core, such as flexibility and toughness. Itmay be possible to use inexpensive plasticizers such as sugar andsorbitol. Such other materials will be readily recognized by thoseskilled in the art and are commercially available from a number ofsuppliers.

A plasticizer, if used, would also generally be added to the formulationin an amount of about 0.1 to 4 wt. percent, more usually about 1 to 2wt. percent, of the total weight of the building material composition(that is percent by weight of the dry solids used in forming thecomposition).

The building material composition, e.g., the fire door core of thepresent invention may contain still other optional components as long asthese other components do not adversely affect the advantageousproperties, especially the fire resistant property, of the composition,e.g., the fire resistant property of the fire door core, of the presentinvention. For example, another optional ingredient is diatomaceousearth. Diatomaceous earth is predominately silica and is composed of theskeletal remains of small prehistoric aquatic plants related to algae(diatoms). Particles of diatomaceous earth typically have intricategeometric forms. The irregular particle shapes are believed to improvethe overall binding of the composition together and the resultantstrength of the composition. Generally, the amount of such otheroptional components, such as the diatomaceous earth is less than about10 weight percent of the building material composition, e.g., the firedoor core. In the case of the diatomaceous earth in particular, whenused the diatomaceous earth will generally be used in an amount of fromabout 1 to 10 weight percent, more usually from about 2 to about 8weight percent and most often from about 3 to about 6 weight percent ofthe building material composition, e.g., the fire door core. The amountof these optional components is preferably less than about 10 weightpercent, even more preferably the amount is less than about 5 weightpercent.

The continuous roll press method is one known process of making thebuilding material composition of the present invention and especiallyfire door cores. Illustrative of the known roll method is the methoddescribed in U.S. Pat. No. 5,256,222, the disclosure of which isincorporated herein by reference. A non-solid (aqueous) mixture of thecomponents of the composition, e.g., fire door core, is deposited onto amoving web drawn from a supply roll by pull rolls. Then, another movingweb drawn from its own supply roll by pull rolls is directed by guideand press roll(s) onto the top of the mixture. The thickness of thesandwich of fire door core mixture and webbing then is reduced to adesired value by roll-pressing. The roll molded fire door core then istransported by known industrial methods to a drying area (such as anoven). The drying of the roll molded fire door core can be achieved atambient temperature or by using drying equipment that operates at atemperature greater than room temperature.

In accordance with a semi-continuous batch press mold method, theingredients of the building material composition, e.g., the fire doorcore and water, are mixed in a suitable mixing device to produce the wetmixture, e.g., the wet door core mixture. Mixing devices suitably usedin this step of the process are well known to skilled practitioners.Preferably, the dry ingredients are mixed with an amount of water nogreater than that required to provide a damp (moist) mixture of theingredients and then the moist (damp) mixture is then molded andcompressed to form the composition or core as described below. It ispreferred that the ingredients of the composition, e.g., the fire doorcore ingredients, be mixed in a manner such that the expanded perlite issubstantially unbroken. In order to substantially eliminate the breakingof the expanded perlite during mixing, preferably the other componentsof the composition, e.g., the other fire door core ingredients, aremixed together first. This allows the expanded perlite to thoroughlyblend with the other ingredients with a minimum of mixing. The amount ofexpanded perlite broken during the mixing process can be determined bycomparing the volume of the wet mixture, e.g., the wet door core mixturebefore and after mixing.

The wet mixture, e.g., the wet door core mixture then is transferred toa mold having a shape corresponding to desired composite dimensions.Typically, a door core is molded to form a slab having the dimensions36″×84″×1¾″. The moist mixture transfer step can be accomplished usingany of the techniques well known to skilled practitioners. The wetmixture, e.g., the wet door core mixture then is compression molded tocompact the mixture to the desired density and thickness to produce awet composite, e.g., a wet door core.

The press molding of the present invention can use any means of pressurewell known to those of skilled practitioners and suitable equipment iswell known to the skilled worker. Typically, the level and the durationof the applied pressure is sufficient to bind the ingredients togetherin a composition, e.g., in a door core, that has a density from about 18to about 35 pounds per cubic foot, more usually between about 23 toabout 28 pounds per cubic foot, after drying, while at the same timebeing insufficient to break a significant number of the expanded perliteparticles. It is expected that satisfactory results will be obtained bycompressing the damp mixture to about 25 to about 33% of its originalvolume, utilizing pressures within the range of about 90 to about 170psi for about 15 to about 55 seconds, and more usually about 100 to 130psi. As skilled practitioners will recognize the exact pressure and timerequired will vary for different embodiments of the present inventionand suitable pressure and time schedules can be determined using routinetesting. The wet composite, e.g., the wet door core then is transferredto a drying area.

The wet composite, e.g., wet door core, then is dried (cured) to producethe building material composition, e.g., the fire door core of thepresent invention. The wet composite, e.g., the wet door core is cured(i.e., dried) at a temperature and for a time sufficient tosubstantially eliminate excess water from the wet composite, e.g., fromthe wet door core. Although the drying can be accomplished at ambienttemperature, drying at elevated temperatures may often be preferred. Forexample, drying of the wet composite, e.g., the wet door core, may becarried out at a temperature from about 150° to about 300° Fahrenheit(about 65° to 150° C.), for a time from about 4 to about 8 hours, withlower temperatures requiring longer times. Skilled practitionersrecognize that specific curing times and temperatures will depend on theexact composition of the wet composite, e.g., the wet door core andsuitable temperature and time schedules can be determined using routinetesting.

After the core has been dried, finishing operations can be effected. Forexample, the core can be sanded to a thickness within the requiredtolerance, sawed or shaped as desired. The nature of the dried materialis such that finishing operations can be performed readily.

During the course of finishing operations such as sanding and sawing,core dust is produced. In accordance with this invention, it isanticipated that the dust can be used in preparing other cores byincluding it in the mixture from which the core is made. This isadvantageous because it makes use of a material that would otherwise bewaste requiring disposal. The use of core dust is expected to increasethe density of the core. Accordingly, the maximum amount of core dustused will be governed by the desired density of the core. It isrecommended that the core dust comprise no more than about 6 wt. % ofthe total weight of the dry mixture of ingredients. Preferably, the coredust should comprise no more that about 2 to about 4 wt. % of themixture.

The following non-limiting example further illustrates the invention.

EXAMPLE 1

A door core of the present invention of the following composition can bemanufactured from a mixture of the following ingredients:

Ingredients Amount (dry weight percent) Expanded perlite 70.19 Fastsetting cementitious component 27.31 Comprising a mixture of PortlandCement and a Pozzolan Additive Polyvinyl alcohol 2 Glass Fibers 0.5

The fast-setting cementitious component constitutes a mixture ofPortland cement (OPC) and either metakaolin or VCAS (PA) in a weightratio of (OPC:PA) about 10.4:1.

Water in an amount of about 20-40 weight percent of the dry weight ofthe various ingredients should be added and the door core can beproduced by pressing at about 150 psi and drying (curing) the pressedcore at about 250° F. (120° C.) for about 4-5 hours.

It will be understood that various changes in the details, materials andarrangements of parts which have been herein described and illustratedin order to explain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the appended claims. Unless otherwise specificallyindicated, all percentages are by weight. Throughout the specificationand in the claims the term “about” is intended to encompass + or −5%.

1. A composition useful for producing a fire door core comprising anaqueous mixture of (A) expanded perlite and (B) a fast setting,cementitious component consisting essentially of (1) a hydraulic cementand (2) a pozzolan additive selected from the group consisting of (i)metakaolin, (ii) VCAS and (iii) mixtures thereof, which composition canbe molded and shaped into a fire door core.
 2. The composition of claim1 wherein the hydraulic cement is Portland cement (OPC) and the Portlandcement and the pozzolan additive (PA) are present in the fast settingcementitious composition in a weight ratio (OPC:PA) within the range of3:1 to 30:1.
 3. The composition of claim 2 containing an organic binder.4. The composition of claim 3 wherein the Portland cement and thepozzalan additive are present in the fast setting cementitiouscomposition in a weight ratio (OPC:PA) within the range of 4:1 to 15:1.5. A building material composition useful as a fire door core,comprising a cured aqueous mixture of (A) expanded perlite, (B) a fastsetting, cementitious component consisting essentially of (1) ahydraulic cement and (2) a pozzolan additive selected from the groupconsisting of (i) metakaolin, (ii) VCAS and (iii) mixtures thereof, (C)an organic binder and (D) a fibrous reinforcement, which aqueous mixturebefore curing can be molded and shaped into a fire door core, andwherein said aqueous mixture contains on a dry weight basis about 65 toabout 85 weight percent of the expanded perlite (A), about 15 to about40 weight percent of the fast-setting cementitious component (B), about1 to about 5 weight percent of the organic binder (C), and about 0.2 toabout 1 weight percent of the fibrous reinforcement (D).
 6. The buildingmaterial of claim 5 wherein the hydraulic cement is Portland cement(OPC) and the Portland cement and the pozzolan additive (PA) are presentin the fast setting cementitious component in a weight ratio (OPC:PA)within the range of 3:1 to 30:1.
 7. The building material composition ofclaim 6 wherein the Portland cement (OPC) and the pozzolan additive (PA)are present in the fast setting cementitious composition in a weightratio (OPC:PA) within the range of 4:1 to 15:1.
 8. The building materialcomposition of claim 5 wherein said aqueous mixture contains from about15 to about 60 percent by weight water based on the dry weight ofcomponents (A), (B), (C), and (D).
 9. A building material compositionprepared by drying an aqueous mixture of (A) expanded perlite, (B) afast setting, cementitious component consisting essentially of (1) ahydraulic cement and (2) a pozzolan additive selected from the groupconsisting of (i) metakaolin, (ii) VCAS and (iii) mixtures thereof, (C)an organic binder and (D) a fibrous reinforcement, wherein, on awater-free basis, the expanded perlite (A) comprises about 65 to about85 weight percent of the aqueous mixture, the fast-setting cementitiouscomponent (B) comprises about 15 to about 40 weight percent of theaqueous mixture, the organic binder (C) comprises about 1 to about 5weight percent of the aqueous mixture and the fibrous reinforcement (D)comprises about 0.2 to about 1 weight percent of the aqueous mixture.10. The building material composition of claim 9 wherein the hydrauliccement is Portland cement (OPC) and the Portland cement and the pozzolanadditive (PA) are present in the fast setting cementitious component ina weight ratio (OPC:PA) within the range of 3:1 to 30:1.
 11. A methodfor making a fire door core from an aqueous mixture of materials, whichmethod comprises mixing water, expanded perlite, a fast settingcementitious component consisting essentially of a mixture of hydrauliccement and a pozzolan additive selected from the group consisting ofmetakaolin, VCAS and mixtures thereof, an organic binder and a fibrousreinforcement, wherein, on a water-free basis, the expanded perlitecomprises about 65 to about 85 weight percent of the aqueous mixture,the cementitious composition comprises about 15 to about 40 weightpercent of the aqueous mixture, the organic binder comprises about 1 toabout 5 weight percent of the aqueous mixture, and the fibrousreinforcement comprises about 0.2 to about 1 weight percent of theaqueous mixture, the water being present in an amount in excess of thestoichiometric amount needed to hydrate the fast setting cementitiouscomposition and sufficient to provide a damp mixture but less than anamount which would produce an aqueous slurry of the intermixedingredients, placing a charge of the damp mixture in a pressure mold ofslab form, applying sufficient pressure to the damp charge in the moldto compress the charge to about 25% to 33% of its original volume andmaintaining the pressure until the compression strength of thecompressed charge is at least about 50 psi and up to about 170 psi,removing the molded slab from the mold and thereafter drying the slab byheating it sufficiently to remove excess water, and forming a fire doorcore piece from the dried slab.
 12. The method of claim 11 wherein thehydraulic cement is Portland cement (OPC) and the Portland cement andthe pozzolan additive (PA) are present in the fast setting cementitiouscomposition in a weight ratio (OPC:PA) within the range of 3:1 to 30:1.13. The building material composition of claim 6 wherein the expandedperlite has a density of about 6.5 lb./cu. ft.
 14. The building materialcomposition of claim 6 wherein the organic binder is polyvinyl alcohol.15. The building material composition of claim 14 in which theintermixed ingredients further include unexpanded vermiculite in anamount not greater than about 4 wt. % of the dry ingredients.
 16. Thebuilding material composition of claim 15 in which the intermixedingredients further include clay in an amount not greater than about 4wt. % of the dry ingredients.